Magnetic speedometer.



J. K. STEWART.

MAGNETIC SPEEDOMETER.

APPLICATION FILED MAY 13, 1911.

Patented July 30, 1912.

JOHN K. srrnwnn'r, on CHICAGO, rumors.

MAGNETIC SEEEDOMETER.

Specification of Letters Patent.

Application filed May 13, 1911.

ratemea Jul so, 1912.

Serial No. 627,069.

changes-upon the action of the instrument;

' It consistsof the features and elements shown and described as indicated in the claims,

In the drawings :-Figure 1, is a sectional elevation of a speedometer showing the interior construction embodying this invention, section being taken" as, indicated at line 11, on Fig. 2; Fig. 2 is a section taken at line2-2, on Fig. 1, the magnet being shown with the top cover-plate removed to show the features embodying this invention. Fig. 3 is an enlarged detail plan view of an auxiliary pole-piece and its operating con nections.

As represented in the drawlngs this speedometer is of a comparatively simple and usual type, comprising a case, 1, a driv ing shaft, 2, and a rotatable carrier, 3, adapted to be driven from the shaft, 2, by beveled gears, 2 and '3, of the shaft and carrier respectively. Upon the carrier, 3, there are fixedly mounted a permanent magnet, 4, and a soft iron ring, 5, separated from themagnet by space sufficient to admit a cylindrical portion, 6, of the cup-shaped, non-magnetic disk, 6, 'ournaled co-axially with the carrier. Connected to the spindle, 7, of this disk, there is shown the usual biasing-spring, 8, and indicator, 9. As is well understood, the operation of this typefof instrument depends upon a magnetic drag which acts upon the disk, 6, counter tothe force of its spring, 8, whenever'the magnet, 4, is rotated. It is also well understood that a rise of temperature tends to 'decrease the' electrical conductivity of the' disk, 6, and to occasion a corresponding decrease in the effect of the magnetic drag upon the disk, if the strength of the rotating magnetic field produced by the magnet, 4, remains constant. As shown, the magnet, 4, has the form of a split ring, being almost a complete annulus. The function of the soft ir'on ring, 5, is toconcentrate; the magnetic field about the magnet, 4, in vthe annular space between the magnet and the ring, into which the portion, 6 offthe disk protrudes. Thestrength of this magnetic field in the neighborhood of themagnetdepends on the proximity of its poles, being greater or less according as these poles are separated by a greater or less air gap.

The purpose of the present invention is to overcome the effect of a rise in temperature in decreasing the conductivity of the disk, 6, and the consequent effect of the magnetic drag upon it, by increasing the actual strength of the rotating magnetic field simultaneously with such increase of temperature. This is accomplished by providing the end, 4*, with a movable poleiece, 10,-designed to he always in contact with the end of the magnet, 4, but movable for varying its own distance from the other pole, 4" as shown, it consists of a small piece of metal pivotally carried between two cover-plates, 11 and 12, formed as split rings to fit the'upper' and lower flat surfaces of the magnet. ,The end, 4, of the magnet isnotched sufiiciently to admit the pole-piece, 10, which is carried on a pin, 13, extending through both cover-plates. The cover-plates extend over the notch in the pole, 4*, so as to be always in contact with the upper and lower faces of the polepiece, 10; thus the element, 10, is at all times in elfect one of the poles of the magnet, 4, and the fact that it is a separate piece may be regarded merely as a mechanical expedient for rendering one pole extensible toward the other pole,iso that the air-gap between the polesmay be varied for varying the strength of the magnetic field surrounding the' magnet.

Just under the cover-platepll, there is formed in the magnet an annular channel in which there is fitted a split ring, 14, of copper or other metal having a different 00- eflicient of expansion from that of the steel of which the magnet is made. Thiscopper element is fixed to the magnet by a rivet, 15, shown near the end, 4, the other end of the element, 14, (which is free to move with respect to the magnet under the influence of temperature changes) is formed with a short series of gear teeth, 14, which mesh with a corresponding'segmental gear, 10, out upon the pole-piece',-10, concentrically about its pivot, l3. The radius of'the gear segment,

10*, is so small as compa'red with the total length of the pole-piece, 10, that slight elongationor contraction of the element, 14, is several times multiplied in the movement of the outer end, 10", of the pole-piece.

With the parts arranged as shown, and

assuming'that for a given rise of tempera-' ture theelement, 14, will elongate more than the magnet, 4, it will be seen that such a rlse increased to compensate for its loss of elliciency, and, this is what is accomplished by increasing the -air ga between the poles.

Thus,- when the ratio between the radius of the gear segment, 10, and the length of the portion, 10 of the pole-piece has been properly related to the co-efficient of expansion of the element, l t, as compared with the coeiiicient of expansion of the magnet, the device 1 serves to automatically accommodate the'act-ion to variable conditions of temperature, thus considerably increasing the :accuracy of the instrument.

- I claim 1 .1. In a magnetic speedometer, a magnet, one pole of which comprises a' pole-piece mounted for movement in contact with the magnet body toward and from the other polejof the magnet, and a thermostatic'de vice adapted for-effecting such movementofthe pole-piece.

j 2. In a magnetic speedometer, a rotatably mounted magnet having the for of a split ring one pole being extensible toward the other, and a thermostatic device adapted for eflecting the extension of said pole.

3. In a magnetic speedometer, a rotatably mounted magnet having the form of a split ring, one pole being extensible toward the other, and a split ring of different metallic composition from the magnet and mounted thereon, having one endsecured thereto and having the other end operatively connected with the extensible pole of the magnet.

4 In a magnetic speedometer, a rotatably mounted magnet having the form of a split ring, one pole comprising a pole-piece pivotally connected to the magnet for movmg toward and from the other pole thereof, a split ring of difierent metallic composition from the magnet and mounted thereon, having one end operatively connected with the pivoted pole-piece and having the other end secured to the magnet.

55. In a magnetic speedometer, a magnet having the form of a' split ring, and provided with a pole-piece pivoted at one end thereof, and having gear teeth formed con centrically about its pivot, and a thermo static device fixed to the magnet, having its free movable portion formed with gear teeth adapted to mesh with the gear of the polepiece for moving the latter toward and from the other pole of the magnet.

6. In a magnetic speedometer, a magnet having the form of a split ring and having an annular groove formed in one of its faces concentrically about the axis of the ring, cover-plates secured to two opposite faces of the magnet, the magnet having an auxiliary pole piece mounted between the ring, mountedon the-carrier, a soft iron ring of greater diameter than the magnet, mounted concentrically therewith on the carrier, with an annular space separating it from the. magnet, a non-magnetic element fjournaled co-axially with the carrier and having the form of an inverted cup protruding into the annular space between the magnet and the ring, and a biasing spring'therefor, one end of the'magnet having an auxils iary pole-piece pivotally connected thereto,

the pivot being parallel with the axis of the magnet carrier, and a thermostatic device on the magnet adapted for rotating the polepiece about its pivot.

8. In a magnetic speedometer, comprising a case, a carrier mounted for rotation therein, a magnet having the form of a split ring, mounted on the carrier, a soft iron ring of greater diameter than the magnet, mounted concentrically therewith on the car rier, with an annular space separating it from the magnet, a non-magnetic element journaled co-axially with the carrier and having the form of an inverted cup protruding into the annular space between the magnet and the ring, and a biasing spring therefor, the magnet having an auxiliary pole-piece pivoted between the end of the magnet body at one end of the magnet and in contact therewith, the longer end of the pole-piece extendingfrom its pivot outwardly toward the aforesaid annular space, and a thermostatic device mounted on a magnet in operative connection with the shorter end of the pole-piece.

9, In amagnetic speedometer, comprising a case, a magnet and a non-magnetic disk co-axially journaled therein, means biasing one of them against rotation, and a soft iron ring encircling the magnet-and separated therefrom by an annular air space, one pole of the magnet being extensible toward the other, and a thermostatic device adapted for efiecting the extension of said pole.

10. Ina magnetic speedometer comprising a revolving magnet, an armature mounted near said magnet and separated therefrom by an air gap, a biased non-magnetic element mounted for oscillation in said air gap, one pole of the magnet being extensible toward the other, and a thermostatic device adapted for effecting the extension of said ole. 1 p In testimony whereof I have hereunto set my hand, April 29, 1911; 4

' l OHN K. STEWART.

Witnesses:

LUCY STONE, 'M, GERTRUDE ADY. 

